Ice ages only thanks to feedback

Ice ages and warm periods have alternated fairly regularly in the Earth's history: the Earth's climate cools roughly every 100,000 years, with vast areas of North America, Europe and Asia being buried under thick ice sheets. Eventually, the pendulum swings back: it gets warmer and the ice masses melt. While geologists and climate physicists found solid evidence of this 100,000-year cycle in glacial moraines, marine sediments and arctic ice, until now they were unable to find a plausible explanation for it.

Using computer simulations, a Japanese, Swiss and American team including Heinz Blatter, an emeritus professor of physical climatology at ETH Zurich, has now managed to demonstrate that the ice-age/warm-period interchange depends heavily on the alternating influence of continental ice sheets and climate.

"If an entire continent is covered in a layer of ice that is 2,000 to 3,000 metres thick, the topography is completely different," says Blatter, explaining this feedback effect. "This and the different albedo of glacial ice compared to ice-free earth lead to considerable changes in the surface temperature and the air circulation in the atmosphere." Moreover, large-scale glaciation also alters the sea level and therefore the ocean currents, which also affects the climate.

Weak effect with a strong impact

As the scientists from Tokyo University, ETH Zurich and Columbia University demonstrated in their paper published in the journal Nature, these feedback effects between the Earth and the climate occur on top of other known mechanisms. It has long been clear that the climate is greatly influenced by insolation on long-term time scales. Because the Earth's rotation and its orbit around the sun periodically change slightly, the insolation also varies. If you examine this variation in detail, different overlapping cycles of around 20,000, 40,000 and 100,000 years are recognisable (see box).

Given the fact that the 100,000-year insolation cycle is comparatively weak, scientists could not easily explain the prominent 100,000-year-cycle of the ice ages with this information alone. With the aid of the feedback effects, however, this is now possible.

Simulating the ice and climate

The researchers obtained their results from a comprehensive computer model, where they combined an ice-sheet simulation with an existing climate model, which enabled them to calculate the glaciation of the northern hemisphere for the last 400,000 years. The model not only takes the astronomical parameter values, ground topography and the physical flow properties of glacial ice into account but also especially the climate and feedback effects. "It's the first time that the glaciation of the entire northern hemisphere has been simulated with a climate model that includes all the major aspects," says Blatter.

Using the model, the researchers were also able to explain why ice ages always begin slowly and end relatively quickly. The ice-age ice masses accumulate over tens of thousands of years and recede within the space of a few thousand years. Now we know why: it is not only the surface temperature and precipitation that determine whether an ice sheet grows or shrinks. Due to the aforementioned feedback effects, its fate also depends on its size. "The larger the ice sheet, the colder the climate has to be to preserve it," says Blatter. In the case of smaller continental ice sheets that are still forming, periods with a warmer climate are less likely to melt them. It is a different story with a large ice sheet that stretches into lower geographic latitudes: a comparatively brief warm spell of a few thousand years can be enough to cause an ice sheet to melt and herald the end of an ice age.

Box: The Milankovitch cycles

The explanation for the cyclical alternation of ice and warm periods stems from Serbian mathematician Milutin Milankovitch (1879-1958), who calculated the changes in the Earth's orbit and the resulting insolation on Earth, thus becoming the first to describe that the cyclical changes in insolation are the result of an overlapping of a whole series of cycles: the tilt of the Earth's axis fluctuates by around two degrees in a 41,000-year cycle. Moreover, the Earth's axis gyrates in a cycle of 26,000 years, much like a spinning top. Finally, the Earth's elliptical orbit around the sun changes in a cycle of around 100,000 years in two respects: on the one hand, it changes from a weaker elliptical (circular) form into a stronger one. On the other hand, the axis of this ellipsis turns in the plane of the Earth's orbit. The spinning of the Earth's axis and the elliptical rotation of the axes cause the day on which the Earth is closest to the sun (perihelion) to migrate through the calendar year in a cycle of around 20,000 years: currently, it is at the beginning of January; in around 10,000 years, however, it will be at the beginning of July.

Based on his calculations, in 1941 Milankovitch postulated that insolation in the summer characterises the ice and warm periods at sixty-five degrees north, a theory that was rejected by the science community during his lifetime. From the 1970s, however, it gradually became clearer that it essentially coincides with the climate archives in marine sediments and ice cores. Nowadays, Milankovitch's theory is widely accepted. "Milankovitch's idea that insolation determines the ice ages was right in principle," says Blatter. "However, science soon recognised that additional feedback effects in the climate system were necessary to explain ice ages. We are now able to name and identify these effects accurately."

(Phys.org)—Earth's most recent shift to a warm climate began with intense summer sun in the Northern Hemisphere, the first pressure on a seesaw that tossed powerful forces between the planet's poles until greenhouse gases ...

Global warming five million years ago may have caused parts of Antarctica's large ice sheets to melt and sea levels to rise by approximately 20 metres, scientists report today in the journal Nature Geoscience.

On Mars's poles there are ice caps of ice and dust with layers that reflect to past climate variations on Mars. Researchers from the Niels Bohr Institute have related the layers in the ice cap on Mars's north pole to variations ...

Ice ages are the greatest natural climate changes in recent geological times. Their rise and fall are caused by slight changes in the Earth's orbit around the Sun due to the influence of the other planets. But we do not know ...

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40 comments

From the abstract: "Carbon dioxide is involved, but is not determinative, in the evolution of the 100,000-year glacial cycles."

Al Gore used a literal cherry picker to promote the false claim that carbon dioxide did control ice ages despite it being well known that CO2 merely followed T changes, only acting as a mild positive feedback that trailed T by 800 years:

Al Gore used a literal cherry picker to promote the false claim that carbon dioxide did control ice ages despite it being well known that CO2 merely followed T changes, only acting as a mild positive feedback that trailed T by 800 years:

Nik:I have just scanned the transcipt of "An inconvenient truth" and I find no such statement. I assume you mean it was made in the presentation?

"Here is what the temperature has been on our earth. One thing that kind of jumps out at you is. Let me put it this way. If my class mate from the sixth grade that talked about Africa and South America might have said, "Did they ever fit together?" Most ridiculous thing I ever heard. But they did of course. The relationship is very complicated. But there is one relationship that is more powerful than all the others and it is this."

In other words - that there is a relationship - a "complicated" one but a powerful one. NOT, as your bias suggests, a "control".

Why do keep saying that CO2 is a "mild" +ve feedback. Can you please provide links to studies that indicate that?As +1C for doubling CO2, increasing to +3C (+/-1.5C ) with feed-backs - is certainly not "mild", given that man has increased it by 40% already.

It can be seen that CO2 is in lock step with temp in a warming climate, whilst lagging in a cooling climate.This another example of attempts to discredit the science via distortion and demonisation of (a) certain figure(s) at the forefront of the message. His video was made in 2006 and the science has more answers than then, such as .....http://www.skepti...lag.html

As Gore showed the chart of CO2 and T in his movie he described it thus: "When there is more carbon dioxide the temperature gets warmer."

The non-controversial correct statement would have been: "When the temperature is warmer, carbon dioxide levels rise."

Are you *really* going to link to SkepticalScience.com?! Let's see how comic pane artist and evangelical Christian John Cook's recent "confirmation" of the 97% consensus study has been working out for him:

The highly speculative 3X water vapor amplification of the old school greenhouse effect now stands falsified as Climategate and its aftermath have clearly exposed, quotes of which I will post here too....

Dr. Mojib Latif – Spiegel – 19th November 2009"At present, however, the warming is taking a break,"……."There can be no argument about that,"

Dr. Jochem Marotzke – Spiegel – 19th November 2009"It cannot be denied that this is one of the hottest issues in the scientific community,"…."We don't really know why this stagnation is taking place at this point."

Dr. Phil Jones – BBC – 13th February 2010"I'm a scientist trying to measure temperature. If I registered that the climate has been cooling I'd say so. But it hasn't until recently – and then barely at all. The trend is a warming trend."

Dr. Phil Jones – BBC – 13th February 2010Q: B – "Do you agree that from 1995 to the present there has been no statistically-significant global warming"A: "Yes, but only just".

Prof. Shaowu Wang et al – Advances in Climate Change Research – 2010"…The decade of 1999-2008 is still the warmest of the last 30 years, though the global temperature increment is near zero;…"

Dr. Robert K. Kaufmann – PNAS – 2nd June 2011"…..it has been unclear why global surface temperatures did not rise between 1998 and 2008….."

Dr. Gerald A. Meehl – Nature Climate Change – 18th September 2011"There have been decades, such as 2000–2009, when the observed globally averaged surface-temperature time series shows little increase or even a slightly negative trend (a hiatus period)…."

Met Office Blog – Dave Britton (10:48:21) – 14 October 2012"We agree with Mr Rose that there has been only a very small amount of warming in the 21st Century. As stated in our response, this is 0.05 degrees Celsius since 1997 equivalent to 0.03 degrees Celsius per decade."

Dr. James Hansen – NASA GISS – 15 January 2013"The 5-year mean global temperature has been flat for a decade, which we interpret as a combination of natural variability and a slowdown in the growth rate of the net climate forcing."

Dr. Hans von Storch – Spiegel – 20 June 2013"…the increase over the last 15 years was just 0.06 degrees Celsius (0.11 degrees Fahrenheit) — a value very close to zero….If things continue as they have been, in five years, at the latest, we will need to acknowledge that something is fundamentally wrong with our climate models…."

Professor Rowan Sutton – Independent – 22 July 2013"Some people call it a slow-down, some call it a hiatus, some people call it a pause. The global average surface temperature has not increased substantially over the last 10 to 15 years,"

Background on John Cook who runs the propaganda site SkepticalScience.com, which allows initial skeptical comments followed by bans that create the false appearance that skeptics have bowed out of a topic in defeat, as the original post is then edited too. John Cook's political motivation is revealed in his book:

"A sustainabl­e society will require fairness (equity) and justice locally and globally, both within this generation and between our generation and future generations." – John Cook

"Preventin­g the collapse of human civilizati­on requires nothing less than a wholesale transforma­tion of dominant consumer culture." – John Cook

"Just because there a professor of something denying climate change does not mean it is not true, it is just that the professor is in denial. This is why one must make use of the prepondera­nce of evidence in science, the collective view." – John Cook

djr: Do you here publicly agree with John Cook's truly creepy doublespeak attempt to equate preponderance of evidence with dehumanizing mob rule, in a book for laypersons? Do you support the slander of critics as being oxymoronic "climatic change deniers?"

Do you feel that sincerely expressed evidence of the biggest scientific fraud of all time has no place on a science blog, in a thread populated by the likes of UK Met Office associates whose office depends on climate alarm to obtain multimillion dollar grants?

Argument from ignorance about what caused recent warming does not represent evidence, let alone a preponderance of it. Studies of how recent mostly natural warming effects animal migration does not represent evidence in support of man made Global Warming, nor do polar ice variations in which Antarctica has been growing for decades.

WHAT PREPONDERANCE OF EVIDENCE?! Your side of this "debate" never presents that evidence, and never has. There would be almost no mainstream skepticism, no twenty thousand daily readers of skeptical blogs if you did have serious positive evidence that recent warming is outside of natural variation. What skeptics have found though is a preponderance of evidence that climate science has been corrupted by agenda driven funding that creates bogus hockey sticks and vigorously punishes dissent.

Is the simple average of world tide gauges by Church & White a yoga pretzel?:

As Gore showed the chart of CO2 and T in his movie he described it thus: "When there is more carbon dioxide the temperature gets warmer."The non-controversial correct statement would have been: "When the temperature is warmer, carbon dioxide levels rise."

Nik:It may be "controversial" to you - but not to the scientific community. The temperature does indeed rise when CO2 levels rise. Just as as CO2 rises when temperature rises. The premise of "An inconvenient truth" came from anthropogenic warming and hence, though they both are true - it's the former that's the problem.

Are you *really* going to link to SkepticalScience.com?!

Yes I will, if I have to pay $32 otherwise! - I actually linked to a paper ( Shakun et al. Clarify the CO2-Temperature Lag) released last year, that is available there in part. If you like go here and pay $32 > http://www.nature...915.htmlOn the blogs you read it of course wouldn't feature.

The highly speculative 3X water vapor amplification of the old school greenhouse effect now stands falsified as Climategate and its aftermath have clearly exposed, quotes of which I will post here too....

As I said to you just this week - WV amplification is ~2 and it only stands falsified in the minds of deniers. I await the papers that show otherwise.So you are also a conspiracist? How does that stand with your scientific training? Don't you have a logical mind? doesn't it tell you that that notion is beyond bizarre. Were you not taught the meaning of probabilities? In your mind the scientists at Norwich were part of a massive falsification of data ( must be as it has to match the many other scientists that found the same thing ). Don't bother with any so-called quotes - as they are out of context and we are ignorant of their "verbal short-hand" ( which is of course the logical explanation ).

I never took any liberal arts courses in thirteen years of college except French, scientific writing and theater, and today I am finally learning that "affect" isn't just emotion and that "effects" only refers to final goals being realized. No wonder I stuck to science!

I think Gore's jet ski, you know the jet ski that needed extra gas to support his love of steaks and potatoes, the jet ski that can circle his monstrous party yacht parked near his six fireplace gangster movie worthy ocean view palace, or is it near the other huge estate he jet sets to, that jet ski that Al Gore owns, I believe can be found by searching Google for "Gore's Boat."

Skeptics not only voluntarily photographed each and every one of thousands of temperature stations around the world and rated their adherence to standards, but we also found Gore's jet ski.

James Hansen's right hand man at NASAs little office above Tom's Diner, four blocks from me here at Columbia University, Gavin Schmidt has words about your disqualification as a serious debater due to your use of the term "denier":

I take that as a slander on me and demonisation by association - classy.

FYI: I retired from the UKMO 7 years ago next month. It is primarily a national weather forecasting service within the Ministry of Defence - which is what I did - briefing RAF pilots on low level and station weather then commercially producing public/aviation forecasts. I am proud of the work I did and the lives I may have saved with that advice.

From Wiki: "The Met Office employs over 1500 staff, with approximately 200 working in its climate research unit"

THE UKMO is also one of only two World Area Forecast Centres (WAFC) - the other is WAFC Washington (NOAA).

The difference is quite astounding. This revision was quietly edited online on Christmas Eve. After twelve of thirteen years of over-hot forecasts, now perhaps they will stop leading the weather up a hill?

Shakum appears in depth EIGHT times on the most popular science blog on the Internet, the skeptical clearing house WattsUpWithThat:http://wattsupwit...s=shakun

No, it doesn't, it features as a critique - just as it does in Skeptical - however if I see those websites on my Google page I ignore, as I know that the science is not presented in an unbiased fashion.So I am am merely doing what you do, yes ( as you would view it )?

You said; "Are you *really* going to link to SkepticalScience.com?"I'd say that with knobs on for the Blogs you linked.Don't be a hypocrite. It's a very unedifying trait.

"Have I wasted my time, here? Because, while the species of sincere, conservative-but-rational AGW Skeptics does exist (I know several, and kind-of qualify as one, myself), they turn out to be rare. For the most part, those calling themselves "climate skeptics" are nothing but fully-imbibed Denialists, who wallow in anecdotes and faux-partyline talking points, participating in something that is far more insidious and devastating to our civilization than mere Energy Company Propaganda.

As I have suggested elsewhere, the real purpose of it all may be to undermine the very notion of expertise in our civilization, leaving no strong force to challenge any ruling elite. But whatever the underlying purpose, one result is clear: Tens of thousands of Denialists egotistically assume that their fact-poor, pre-spun, group-rage opinion entitles them to howl "corrupt fools!" at the men and women who have actually studied and are confronting this important topic."http://www.davidb...ge2.html

In short anyone who continually misrepresents the science, even when repeatedly shown to be wrong and resorts to vilification of people rather than their message and above all resorts to bizarre conspiracy theory.......

Interesting, it's nice to understand the (history) of the word around us a little better.Also interesting to note that the scientific community at the time rejected the correct explanation, perhaps also something to learn from.

Professor James Lovelock says that the sun converts hydrogen into helium. Helium is a greenhouse gas for the sun. In 4.5 billion years the sun has heated up 35%. The Earth has maintained it's temperature (amongst many other parameters) constant by sequestering carbon out of the atmosphere. As the temperature increased, so more carbon dioxide was removed. We are now down to the last 4%. Our most efficient CO2 scrubbers, the C4 plants, cannot remove any more.This negative feedback loop is now failing. This is why the recent (Geologically speaking) temperature fluctuates so much.What we are watching is typical of the failure of a feedback loop. Hence the sensitivity.Now that is on topic!

When a climate scientist says that a short period of years yields weak statistical evidence of warming, the problem is the short base period, not the lack of warming. You need longer base periods (e.g. more years of data) to get the sigmas up.

Denialists read it as 'low sigmas, therefore no trend.'

I won't call denialists 'stupid.' Statistics is a subject not everyone has mastered. But they *are* talking out of their ass.

1. "the tilt of the Earth's axis fluctuates by around two degrees in a 41,000-year cycle."2. "Moreover, the Earth's axis gyrates in a cycle of 26,000 years, much like a spinning top."

Isn't 1. and 2. the same thing?

No, not quite the same. The tilt is the angle the earth presents during each orbit around the sun. The tilt is relatively stable and the earth precesses around the tilt (your number 2). There is also nutation (which is about an 18 year cycle) where the earth kind of nods during precession due to the influence of short term torques such as the tides. On a top these things take place very quickly compared to the earth so we would never notice any of them without extremely precise measurements. However, the earth notices as different tilts change the aspect with the sun.

Actually, I believe they were created by Nik, if I'm not mistaken, for purposes of demonstrating the sockpuppetry that he believed others engaged in, rather than confront the idea that he might be not as popular as he appears to be on Breitbart et al.

"As Australians sweltered through a record-breaking summer heatwave this week, one of the world's leading scientific bodies revised down its five-year projection for the world's average temperature." - Pure Ignorance

NikkieTard and Pure Ignorance simply can't distinguish the difference between weather fluctuations and climate change, even though it has been explained to him several dozen times.

The chemical imbalance in his brain that is impairing his thinking is quite profound.